Abstract:With the excellent performance of fertilizer synergist, polyaspartic acid (PASP) may have an effect on the physiological metabolism and nitrogen use efficiency of flue-cured tobacco, which will solve the problems of excessive nitrogen application and low nitrogen use efficiency in tobacco-planting, and provide some reference to the application of PASP in tobacco production. A pot experiment which took the flue-cured tobacco called ‘Yun 87’, and yellow soil, the typical soil of Guizhou Province, was carried out to explore the effects of PASP on the physiological characteristics of tobacco and the fate of nitrogen fertilizer when reducing nitrogen application by 15N-isotope tracer technique. The results indicated that the reduction of nitrogen fertilizer (30%).and the addition of PASP could effectively improve the utilization rate of nitrogen fertilizer, the improvement effect of N reducing was particularly obvious in the late growth stage of flue-cured tobacco, and PASP application could further enhance the improvement effect. With 30% reduction of nitrogen fertilizer application, the root physiology and leaf photosynthetic characteristics of flue-cured tobacco were significantly affected. Under the same conditions, adding PASP significantly promoted root physiology, leaf physiological morphology and nitrogen use efficiency of flue-cured tobacco. The low level PASP(100 mg/pant)didn't showed significant promotion effect on photosynthetic characteristics of flue-cured tobacco roots and leaves, even though it improved nitrogen utilization rate to some extent. Conversely, the high-level PASP (400 mg/pant)were more conducive to the physiological metabolism of roots and leaves of flue-cured tobacco and increased fertilizer use efficiency. In addition, the result of correlation analysis indicated that there was a significant positive correlation between PASP addition and nitrogen use efficiency (p<0.01).Furthermore, the application of PASP significantly increased the total recovery of nitrogen fertilizer, and for tobacco plant, the 15N distribution of aerial part was higher than that of underground part in all treatments during the late growth stage, both of them became higher with the increase of PASP. In conclusion, the application of PASP facilitated the physiological metabolism of flue-cured tobacco, N absorption, and minimize nitrogen loss, especially in the treatment of N reduced by 30% + PASP 400 mg/plant.